4395
NOTES
to be able to discover the slight curvature in a plot of P against T . Work is in hand to extend these measurements to other simple liquids, including polar compounds,
and to high molecular weight polymers, on which some preliminary results have been already published. Acknowledgment. It is a pleasure to acknowledge the continuous interest of Prof. C. Rossi in this work.
NOTES
Barium-Iron-Oxygen Compounds with Varying Oxygen Content and Iron Valence
by Anna Clyde Fraker Department of Engineering Research, North Carolina State University at Raleigh, Raleigh, North Carolina (Received M a y $4, 1966)
The hypothesis of Erchak and Wardl that bariumiron-oxide can accommodate different amounts of oxygen and that the Eitructure maintains stability by varying iron. valencies is supported by this paper, and a correlation between oxidation state and interatomic spacing is shown. Mossbauer measurements'Z of the perovs:kite BaFe03compound reported by Derbyshire, Fraker, and Staclelmaier3 show that 76% of the iron is in the f4 valence state and 24% is in the +S state. Thus the empirical formula for this compound is probably Ba(Fe3+4.Fe.+3)02.9 instead of the stoichiometric BaFe03. Two +3 iron ions are formed for every oxygen ion which is lost. The X-ray pattern of BeFe02.9 is shown in Figure 1A along with charts of two other materials which were equilibrated as described in Table I. The Mossbauer absorption spectrum of preparation A, Table I, as well as a mixture of preparation B and C is shown in Figure 2. I n Figure 2A, the principal absorption peak corresponds to F'e+4, the minor peak to Fe+a, It is characteristic of these structures that their principal diffraction lines coincide and have comparable intensities. The :X-ray patterns of materials E and C show a remarka'ble shift of the diffraction lines due to changes in the experimental conditions. This shift is associated with variations in ionic distances in the basic structure and must be attributed to the ionic radius of the iron. It i s the size of the iron ion inside the octahedron which d.etermines the lattice parameter
shift in the close-packed arrangement of barium and oxygen ions. The Fe-0 distance which is listed in Table I was determined by dividing the interplanar spacing for the strongest diffraction peak by fi. This peak corresponds to { l l O ) planes for the cubic structure of Figure 1A. It may be concluded from Table I that materials B and C are oxygen deficient, and Mossbauer measurements (Figure 2) of a mixture
WK-
C
I (1) M. Erchak, Jr., and R. Ward, J. Am. Chem. Sac., 68, 2093 (1946). (2) Dr. Uri Shimony of the Massachusetts Institute of Technology,
Cambridge, Mass., did the Mijssbauer work. (3) S. W. Derbyshire, A. C. Fraker, and H. H. Stadelmaier, Acta Cryst., 14, 1293 (1961).
Yalume 69, Number 18 December 1966
NOTES
4396
Table I" A
Calcination temp. and atmosphere
1000" in closed tube or 700" in air Barium-iron( IV) oxide and BaCOs Fe +4 0.58 1.98 A. 2.01 A. 76% Fe+4 24% Fe+8
Phases present Valence and radius of iron ion Sum of radii, Fe-0 Distance Fe-0, obsd. Mossbauer measurement of iron valence
4.
B
C
850-900" in air and quenched
950-1000" in air and quenched
Barium-iron( 111) Barium-iron( 11) oxide and oxide and BaO BaO Fe +2 Fe +a 0.64 1 . 0.76 A. 2.04A. 2.16 A. 2.05 h;. 2.10 A. A mixture of materiala B and C shows equal amounts of +3 and +2 iron
a The ionic radii in this table are those of Pauling and the oxygen radius is 1.40 h;. with the exception of the Fe+*radius which is that assumed by C. Brisi, Ann. chim.,45,431 (1955).
in these compounds, and this loss is compensated by the changing valence of the iron ion. As the oxygen loss occurs, the iron is reduced; however, upon reintroduction of oxygen to the structure, the iron again changes to a higher oxidation state. Since this is a reversible process, the material will tend toward an equilibrium compound for a given temperature and given oxygen partial pressure. This reversibility has been observed by taking material of Figure 1C and placing it into the furnace at 1000" in air and allowing it to cool slowly. The resultant structure is that of Figure 1A. (4)W. S. Clabaugh, E. M. Swiggard, and R. Gilchrist, J . Res. Natl. Bur. Std., 56, 289 (1956).
-1.5
1.0
.5
0
.5
1.0
1.5
i2.0
rnrnlsec,
Figure 2.
of B and C show that no f 4 iron is present in either of them. The discrepancy in the observed and calculated Fe-0 distances in material A would also suggest that all iron is not in the f 4 state. Prior to calcination, the materials were prepared by a modified method of Clabaugh, Swiggard, and Gilchrist4 in which a mixed oxalate was precipitated. The initial ratio of barium to iron was 1.5:l. The excess barium is needed to make the reaction go to completion and some of this extra barium is washed out and any remaining excess later comes out as barium oxide or barium carbonate after calcination. Calculated X-ray intensities3 show that the excess barium does not remain as part of the barium-iron-oxygen compound. An increase in temperatufe causes an oxygen loss The Journal of Physical Chemtktru
The Hg( SP&Sensitized Decomposition of n-Hexane Vapor
by Robert R. Kuntz Department of Chemistry, University of Mksouri, Columbia,Missouri (Received June 4, 1966)
The Hg( 3P~)-sensitizeddecomposition of alkanes leads to alkyl radicals and hydrogen atoms. Comparison of the liquid and vapor phase decompositions of npentane1v2and isopentane2vsindicates that similar processes are in operation in these media. The dispropor(1) R.A. Back, Trans. Faraday Soc., 54, 612 (1958). (2) R. R. Kunts and G. J. Maina, J . Am. Chem. Soc., 85, 2219 (1963). (3) R.R.Kuntz, J. Phys. Chem., 69,2291 (1965).
